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Chapter 13: Problem 84

An isotonic solution is described as \(0.92 \%\) NaCl (mass/volume). Would this also be the required concentration for isotonic solutions of other salts, such as \(\mathrm{KCl}, \mathrm{MgCl}_{2},\) or \(\mathrm{MgSO}_{4} ?\) Explain.

Short Answer

Expert verified
No, the concentration for isotonic solutions of different salts will be different. This is because when salts dissolve in water, they dissociate into a different number of ions, which impacts the osmotic pressure of the solution. Hence, different mass concentrations would be required for different salts to achieve isotonicity.

Step by step solution

01

Understanding the Dissolution of Different Salts

Dissolution of Salt in water can have different number of ions. For example, when NaCl dissolves in water, it dissociates into two ions: Na+ and Cl-. KCl also dissociates into two ions: K+ and Cl-. However, salts like MgCl2 and MgSO4 dissociate into three and this makes a difference. MgCl2 dissociates into Mg++ and 2Cl-, while MgSO4 dissociates into Mg++ and SO4--. Therefore, an isotonic solution would require less concentration of MgCl2 and MgSO4.
02

Calculating Molar Concentration of NaCl

Calculate the molar concentration of NaCl in a 0.92% NaCl solution. The molecular weight of NaCl is 58.44 g/mol. Therefore, 0.92 grams of NaCl is approximately 0.0157 moles. Considering the solution is 1 liter, then the molar concentration of NaCl in the solution is 0.0157 mol/L.
03

Projection for Other Salts

As isotonic solutions have the same molar concentration, to determine the required concentration for isotonic solutions of KCl, MgCl2, and MgSO4, use the molar concentration of NaCl (0.0157 mol/L), remember that MgCl2 and MgSO4 would need less concentration to maintain isotonicity due to their higher rate of dissociation. This means the mass of the other salts needed to achieve the same molar concentration will be more for KCl and less for the other two salts.
04

Explanation based on calculations

No, the same mass concentration does not make an isotonic solution. Because different salts dissociate to different numbers of ions per formula unit in solutions, the concentration needed for isotonicity depends not only on the molar concentration but also on the total number of ions that the solute produces in solution.

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